New inorganic-organic hybrid materials based on SBA-15 molecular sieves involved in the quinolines synthesis

Article abstract of DOI:10.1016/j.cattod.2011.12.015

In this paper we report on the first mesoporous catalyst based on SBA-15 incorporating simultaneously basic and acid functions able to promote the Friedl?nder reaction between 2-aminoaryl ketones and ethyl acetoacetate leading to quinolines 1 with high yi

Full text of DOI:10.1016/j.cattod.2011.12.015

Catalysis Today 187 (2012) 97–103
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Catalysis Today
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New inorganic–organic hybrid materials based on SBA-15 molecular sieves
involved in the quinolines synthesis
Jesús López-Sanza, Elena Pérez-Mayorala,∗, Elena Sorianob, Marina Sturma, Rosa María Martín-Arandaa,
a
c,d,∗∗
ˇ
Antonio J. López-Peinado , Jirˇí Cejka
a Departamento de Química Inorgánica y Química Técnica, Facultad de Ciencias, UNED, Paseo Senda del Rey 9, 28040 Madrid, Spain
b Laboratorio de Radicales Libres y Química Computacional (IQOG, CSIC), C/Juan de la Cierva 3, 28006 Madrid, Spain
c Department of Synthesis and Catalysis, J. Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejsˇkova 3, 182 23 Prague 8, Czech Republic
d King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2011
Received in revised form 1 December 2011
Accepted 9 December 2011
Available online 14 January 2012
In this paper we report on the first mesoporous catalyst based on SBA-15 incorporating simultaneously
basic and acid functions able to promote the Friedländer reaction between 2-aminoaryl ketones and
ethyl acetoacetate leading to quinolines 1 with high yields. From 2-aminobenzophenone (3a) it is possi-
ble to prepare quinoline 1a with the highest selectivity (86%) as compared with other mesoporous acidic
catalysts. In contrast, the reaction catalyzed by amine-grafted SBA-15 yielded selectively (98%) the corre-
sponding quinolone 2a in accordance with our previous results. Experimental results have been justified
by theoretical calculations as function of the stability of reaction intermediate species, which could be
involved in the process.
Keywords:
Mesoporous molecular sieve
Heterogeneous catalysis
Quinolines
© 2011 Elsevier B.V. All rights reserved.
SBA-15
1. Introduction
main advantages of ordered mesoporous solids in catalysis are (i)
relatively large pores as compared with microporous materials like
Development of new materials, among them those based on
mesoporous structures, involved in green chemical processes is a
current and challenging topic of fundamental importance in the
design of novel and more efficient environmental friendly cata-
lysts [1]. Discovery of silica-based mesoporous materials attracted
the attention of many researchers since the development of these
types of molecular sieves contributed to extending the range from
microporous and ordered zeolitic materials into the mesoporous
regime [2]. However, these ordered mesoporous materials show
neutral silica frameworks considerably limiting their applications
in catalysis. In order to transform those in supports potentially use-
ful as catalysts, it is necessary to introduce catalytic functions often
by incorporation of organic functional moieties bound into their
walls or by deposition of active species on their inner surface or to
use layered zeolites with large accessible external surfaces [3]. The
zeolites, facilitating the reactants/products diffusion, and (ii) very
high surface areas allowing the introduction of high concentrations
of active sites. Both these features contribute to increase over-
all reaction rates of catalytic processes catalyzed by mesoporous
molecular sieves.
Recently, we reported on the synthesis of quinolines 1/quinolin-
2(1H)-ones 2 via Friedländer reaction (Scheme 1) by condensation
of 2-aminoaryl ketones 3 with ethyl acetoacetate 4, in toluene at
373 K, promoted by acid or basic mesoporous catalysts such as
amino grafted MCM-41, Al(SBA-15) and also zeolites [4]. While
the condensation catalyzed by acid catalysts yielded mixtures of
corresponding quinolin-2(1H)-ones 2 and quinolines 1, dramatic
selectivity changes were observed when using amino grafted MCM-
41 materials. Quinolones 2 were isolated with quantitative yield
and total selectivity.
Friedländer condensation is considered an economic atom reac-
tion consisting of a double condensation between 2-aminoaryl
carbonyl compounds with other carbonyl compounds, exhibit-
ing enolizable hydrogens. It is useful and the simplest synthetic
approach for the preparation of substituted quinolines [5]. These
nitrogen heterocycles represent important substrates in medicine,
food, catalyst, dye, materials, refineries and electronics [6].
From a green chemistry point of view, only a few heterogeneous
catalysts have been reported to be active in Friedländer reaction,
∗
Corresponding author. Tel.: +34 91 398 9047; fax: +34 91 398 6697.
Corresponding author at: Department of Synthesis and Catalysis, J. Heyrovsky´
∗∗
Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i.,
Dolejsˇkova 3, 182 23 Prague 8, Czech Republic. Tel.: +420 26605 3795;
fax: +420 28658 2307.
E-mail addresses: eperez@ccia.uned.es (E. Pérez-Mayoral),
ˇ
jiri.cejka@jh-inst.cas.cz (J. Cejka).
0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2011.12.015

98
J. López-Sanz et al. / Catalysis Today 187 (2012) 97–103
Scheme 1. Friedländer reaction of 2-aminoaryl ketones and ethyl acetoacetate.
detail, to a suspension of dried SBA-15 (2 g) in toluene (35 mL),
(3-aminopropyl)trimethoxysilane (6.65 mmol, molar excess) was
added and the mixture was stirred for 5 h at room temperature
(296 K). Then, toluene was filtered off and the modified SBA-15
was washed out three times with toluene (20 mL). Finally, the SBA-
15/AP was dried in vacuum at room temperature (Scheme 2).
2.1.3. Synthesis of SBA-15/APS
SBA-15/APS was prepared from SBA-15/AP by reaction with ␥-
sultone (Scheme 2). Then, to a suspension of SBA-15/AP (0.5 g) in
toluene (20 mL), ␥-sultone (5 mmol) was added and the reaction
mixture was stirred for 24 h at 363 K. After cooling to ambient tem-
perature, the modified SBA-15 was filtered off and washed out
three times with toluene (20 mL). Finally, SBA-15/APS was dried
in vacuum at room temperature (Scheme 2).
Fig. 1. Mesoporous materials named SBA-15/S.
namely Al2O3 [7], H2SO4/SiO2 [8–10], NaHSO4/SiO2 [11,12],
HClO4/SiO2 [13], silica gel-supported phosphomolybdic acid [14],
KAl(SO4)2·12H2O/SiO2 [15], sulfonated cellulose [16] and silica-
propylsulfonic acid [17]. In this sense and contributing to the
development of new and efficient mesoporous catalysts for this
transformation, we recently communicated on the first example
of Friedländer reaction promoted by a Metal-Organic-Framework,
[Cu3(BTC)2] showing superior activity [18].
2.2. Characterization of the catalyst
Our present interest is focused on the synthesis and characteri-
zation of new inorganic–organic hybrid mesoporous material based
on SBA-15 showing bifunctional organic linkers simultaneously
incorporating basic and acid sites, more specifically, amine groups
and sulfonic acids. In this paper, we also report on its catalytic per-
formance in the Friedländer reaction between 2-aminoaryl ketones
and ethyl acetoacetate, useful synthetic methodology for the prepa-
ration of quinolines.
2.2.1. Nitrogen adsorption
Adsorption isotherms of nitrogen at 77 K on molecular sieves
under study were recorded using a static volumetric apparatus
ASAP 2020 (Micromeritics). In order to attain a sufficient accu-
racy in the accumulation of the adsorption data, this instrument
is equipped with pressure transducers covering the 133 Pa and
133 kPa ranges. Before each sorption measurement the samples
were outgassed at 383–393 K overnight until the residual pressure
was lower than 0.7 Pa. Table 1 lists some characterization data of
the catalysts under study.
2. Experimental
2.1. Synthesis of the catalysts
2.2.2. Thermal stability
Thermal stability of the solids based on SBA-15 structure was
investigated by TG experiments using a TA Instrument SDT Q600.
SBA-15 was synthesized according to the methodology previ-
ously reported [19].
2.1.1. Synthesis of SBA-15/S
SBA-15/S was prepared starting from SBA-15 support by
reaction with 3-(triethoxysilyl)propane-1-thiol and subsequent
oxidation of the thiol group with hydrogen peroxide following the
experimental protocol reported by Pérez-Pariente et al. [20] (Fig. 1).
2.2.3. X-ray diffraction (XRD)
The structure of all synthesized materials was confirmed by X-
ray powder diffraction with a Seifert C-3000 diffractometer with
filtered Cu K␣ radiation in the Bragg-Brentano geometry operating
at 40 kV and 30 mA, over powder samples. X-ray powder diffrac-
tion patterns of all mesoporous materials provided clear evidence
of their hexagonal structure and phase purity of samples under
investigation.
2.1.2. Synthesis of amino-grafted SBA-15, SBA-15/AP
Amino-grafted SBA-15 materials were synthesized according
to the experimental procedure reported in Ref. [21] starting from
SBA-15 support and using trialkoxysilylpropylamine. In more
Scheme 2. Preparation of SBA-15/APS.

J. López-Sanz et al. / Catalysis Today 187 (2012) 97–103
99
Table 1
Characterization data of the mesoporous materials based on SBA-15.
Catalyst
SBET (m2/g)
Da (Å)
Va (m3/g)
Cb (mmol/g)
Nb (mmol/g)
Sb (mmol/g)
SBA-15
834
556
292
254
56
55
55
53
0.97
0.78
0.49
0.48
–
–
–
1.69
1.40
–
0.50
–
SBA-15/S
SBA-15/AP
SBA-15/APS
2.18
5.71
8.89
1.42
SBET, BET surface area. D and V diameter and volumen of the pores, respectively.
a
Determined by BJH method.
Determined by elemental analysis.
b
Reaction products were characterized by 1H NMR. Spectroscopic
data of the synthesized products are according to those previously
reported [4].
2.3. Catalytic activity
2.3.1. General
NMR spectra were recorded with a Bruker AVANCE DPX-300
(300 MHz for 1H). 1H chemical shifts (ı) in DMSO-d6 are given from
internal tetramethylsilane.
2.4. Theoretical calculations
TLC chromatography was performed on DC-Aulofolien/Kieselgel
60 F245 (Merck). All reagents and solvents were purchased from
Aldrich and Alfa-Aesar.
All calculations were performed with the Gaussian 03 suite of
programs [22]. Geometry optimizations were performed using the
B3LYP [23] density functional method in conjunction with the 6-
311G(3d,2d) basis set. They were verified to have all real harmonic
frequencies by frequency calculations, which also provided thermal
corrections to enthalpy.
The electron population analysis was performed on the opti-
mized structures of the reactants 3a,b with the Atomic Polar Tensor
(APT) model [24] because it is relatively independent of the level
of theory.
Each isomer of the presumed key intermediate 6 (see Scheme 3)
was subjected to conformational searching at the B3LYP/6-
311G(3d,2p) level in order to identify the lowest-energy isomer.
The conformational preferences of linear model molecules were
examined through the multidimensional conformational analysis
2.3.2. Experimental procedure
Prior to the reaction catalysts were activated at 363 K for 5 h.
In a typical procedure, the catalyst (25 mg) was added to a
solution of the corresponding 2-aminoaryl ketone 3 (1 mmol)
and ethyl acetoacetate 4 (5 mmol), at 363 K, and the reaction
mixture was stirred during the time shown in Table 2. After
cooling, DMF (2 mL) was added to the reaction crude and the
catalyst was filtered off. Subsequently, DMF was evaporated in
vacuo.
Reactions were followed by TLC using mixtures of hexane/AcOEt
or CH2Cl2/EtOH as eluents.
Scheme 3. Pathways for the synthesis of quinolines 1/quinolones 2 by using acid and basic mesoporous catalysts.

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J. López-Sanz et al. / Catalysis Today 187 (2012) 97–103
Table 2
Friedländer condensation of 2-aminobenzophenone (3a) and ethyl acetoacetate (4) at 363 K.
Catalyst
Time (h)
Y of 1a (%)
S to 1a
Y of 2a (%)
S to 2a
TON
2857
1571
2333
TOF (h−1
)
SBA-15/APS
SBA-15/AP
3
3
6
3
86
3
2
86
9
2
14
63
96
25
14
95
98
27
952
524
389
SBA-15/S
67
73
10454
3484
Y, yield; S, selectivity.
(MDCA) strategy: all the minima that can be anticipated consid-
ering that each flexible dihedral angle is expected to have three
minima, were constructed by systematic rotation of the single
bonds and subsequently optimized.
XRD patterns for all SBA-15 molecular sieves reported here
showed analogs profiles with well-resolved diffraction lines at low
angles evidencing the hexagonal structure of SBA-15 materials
(Fig. 3).
3.2. Catalytic performance
3. Results and discussion
Molecular sieves described above were tested as catalysts
in the Friedländer condensation using differently substituted 2-
aminoaryl ketones 3 and ethyl acetoacetate 4 under solvent-free
conditions. The reaction between 2-aminobenzophenone (3a) and
ethyl acetoacetate (4), catalyzed by SBA-15/APS, at 363 K, yielded
the quinoline 1a in 62% with high selectivity (84%) after 1 h of
reaction time (Scheme 1 and Fig. 4). Note that the reaction was com-
pleted after 3 h affording mixtures of quinoline 1a and quinolone 2a
in 86 and 14%, respectively (Table 2 and Fig. 4). In contrast, when we
carried out the reaction over SBA-15/AP for 6 h, the corresponding
quinolone 2a was isolated in 92% almost as unique reaction prod-
uct. Only traces (<2%) of compound 1a being obtained. Although
the reaction took place in the presence of toluene as a solvent when
using amino-grafted MCM-41 [4a] and absence of that catalyzed by
SBA-15/AP affording quinolone 2a, yield of 2a being notably higher
when operating under solvent-free conditions (92%).
3.1. Synthesis and characterization of the mesoporous materials
In this work we have synthesized three different mesoporous
materials incorporating basic or acid functions or both of those.
At first, we prepared SBA-15/S containing sulfonic acids as active
catalytic centres according to Ref. [20] (Fig. 1). Amino-grafted SBA-
15/AP was synthesized as starting support for the synthesis of
SBA-15/APS, the last one incorporating both secondary amine and
sulfonic acid groups (Scheme 2).
Specific surface areas of all materials were determined from
nitrogen adsorption isotherms being in a range of 556–254 m2/g; a
decrease in the specific surface area was observed depending on the
function sizes as expected. Then, SBA-15/APS was the mesoporous
material showing the lowest surface area. Diameter and volume
3
˚
of the pores were in the ranges of 56–53 A and 0.78–0.48 cm /g,
respectively (Table 1).
Therefore, we report here on two methodologies allowing
the selective synthesis of quinoline 1a or quinolone 2a from 2-
aminobenzophenone (3a) and ethyl acetoacetate (4) depending on
the used catalyst. When using SBA-15/AP, basic catalyst, quinolone
2a was almost exclusively isolated with high yield whereas in
the reaction catalyzed by SBA-15/APS, the selectivity was inverted
yielding the corresponding quinoline 1a with high yields.
In addition, the condensation of 3a and 4 catalyzed by SBA-15/S
gave, after 3 h of the reaction time, mixtures of compounds 1a and
2a in 67 and 25%, respectively (Table 2).
Turnover number (TON) and turnover frequency (TOF) are
defined as TON = conversion (%) (mmol(substrate))/mmol (catalyst)
while TOF = TON/time (h).
Fig. 4 depicts the yield of quinoline 1a and quinolone 2a vs. time;
note that both compounds, 1a and 2a, are formed at the shortest
Chemical composition of the solids was investigated by elemen-
tal analysis. Slightly higher concentration of S (1.419 mmol/g) in
SBA-15/APS compared with the N content (1.400 mmol/g) suggests
a lower concentration of sulfonic acids, 0.019 mmol/g, distributed
on the surface of the catalyst; therefore, the structure of SBA-15/APS
could be represented as shown in Fig. 2.
Thermal stability of the catalysts was investigated by thermo-
gravimetry (TG), all of them being stable in a temperature range
from room temperature to approximately 473 K. It is important to
note that the thiol and sulfonic acid groups located in the inner
surface on SBA-15/S decompose at different temperatures in accor-
dance with the results reported by Margolese et al. [25] and Trejda
et al. [26]. In this sense, considering the TG measurements and
the composition determined by elemental analysis we calculated
the active site concentration referred to sulfonic acid centres in
SBA-15/S. The concentrations of thiol and sulfonic acid species
in SBA-15/S were approximately 0.15 and 0.35 mmol/g, respec-
tively. Therefore, post-synthesis activation of SBA-15 by treatment
with (triethoxysilyl)propane-1-thiol and subsequent oxidation of
the thiol groups using an excess of hydrogen peroxide provided
the mesoporous solid SBA-15/S containing higher concentration of
sulfonic acids.
SBA-15
SBA-15/S
SBA-15/APS
0,5
1
1,5
2
2,5
3
3,5
4
2θ (degrees)
Fig. 2. Possible structure of SBA-15/APS.
Fig. 3. X-ray diffraction patterns for SBA-15, SBA-15/S and SBA-15/APS.

J. López-Sanz et al. / Catalysis Today 187 (2012) 97–103
101
100
80
60
40
20
0
whereas the process catalyzed by SBA-15/APS led to quinoline 1a
with a higher yield (86%) and selectivity (86%). However, when
starting from 3b, quinoline 1b/quinolone 2b mixture in a ratio 3:2
were isolated.
A
Differences in the 2-aminoaryl ketone 3 behavior might be
related to the different structure and stability of the intermedi-
ate compounds leading to the corresponding reaction products.
In order to explain the experimental results we could consider
two different pathways for the reaction depending on the acid-
base properties of the catalyst (a) basic and (b) acid or bifunctional
mesoporous materials (Scheme 3). While the reaction catalyzed by
amino-grafted MCM-41 in toluene [4a], or SBA-15/AP here under
solvent-free conditions, takes place probably through the interme-
diate 5, which subsequently could provide cyclization affording the
corresponding quinolone 1 (Scheme 3, path a), the process cat-
alyzed by acidic mesoporous materials, (Al)SBA-15 or SBA-15/S
and SBA-15/APS, could start by aldolic (Knoevenagel) condensation
between both carbonyl components in the reactants giving mix-
tures of the corresponding cis–trans isomers 6 (Scheme 3, path b).
Then, subsequent cyclization of cis-6 could afford the correspond-
ing quinolone 2 whereas trans-6 yield quinolines 1.
0
1
2
3
4
5
Time (h)
100
80
60
40
20
0
B
0
1
2
3
4
5
The formation of the quinolines of type 1 bearing a carboxylic
ester and the acidic nature of the catalyst suggest the initial Knoeve-
nagel condensation as operative mechanism. This could be initiated
by the activation of the carbonylic oxygen by the acidic sites of the
catalyst.
Time (h)
Fig. 4. Friedländer reaction of 3a and 4 catalyzed by mesoporous silicates; (A) Yield
of 1a vs. time; (ꢀ) SBA-15/APS, (ꢁ) SBA-15/S, (᭹) SBA-15/AP. (B) Yield of 2a vs. time;
(ꢂ) SBA-15/APS, (ꢀ) SBA-15/S, (ꢁ) SBA-15/AP.
The computational study of the 2-aminoaryl ketones 3a–b
(B3LYP/6-311G(3d,2p)) revealed some relevant properties. The
steric effects in 3a induce the lack of planarity between the ketone
moiety and the aromatic groups (the phenyl plane shows a dihedral
torsion of 27◦ and the aminoaryl moiety 39◦, Fig. 5). The computed
APT charges suggest a more electrophilic carbonyl carbon for 3a
(+1.126) than for 3b (+0.975). The larger charge separation on the
carbonyl group on 3a than on 3b would also favor the interaction of
the C O with the catalytic sites thus promoting the reaction. This
difference may be due to the inductive effect of the R substituent
(Ph vs. Me) and the reduced mesomeric effect in 3a.
On other hand, preliminary mechanistic studies have revealed
some differences in the presumed key intermediates cis- and
trans-6. The conformational analysis performed on each isomer
has revealed the following. Taking into account the most sta-
ble structures for every case, we have observed that all of them
involve an intramolecular hydrogen-bond between the amino moi-
ety and a carbonyl group. In addition, the length of this H-bond is
reaction times in the reaction catalyzed by SBA-15/APS and SBA-
15/S, respectively. However, after 2 h of the reaction, yields of 2a
were approximately 14% and 25% while yield of quinoline 1a was
increased during all studied times.
We
also
investigated
the
condensation
of
2-
aminoacetophenone (3b) with 4 over SBA-15/APS as catalyst
under solvent-free conditions at 363 K. In this case, mixtures
of compounds 1b (62%) and 2b (38%) were isolated after 1 h of
the reaction time. It is important to note that after only 1 h the
reaction was completed but quinoline 1b was isolated with lower
selectivity (62%). Remarkably, after this same time 1 h, quinoline
2a was obtained with also 62% of yield but improved selectivity
(84%) as given in Fig. 1A. Under the same reaction conditions the
condensation between 3b and 4 catalyzed by SBA-15/S led to
compounds 1b and 2b in 39% and 61% of yield after 4 h of reaction
time.
Having in mind all these results, we can affirm that SBA-15/S
was found to be the most active catalyst, as demonstrated by the
TON and TOF values shown in Table 2, whereas SBA-15/APS was
the most selective catalyst in the Friedländer reaction between 3a
and 4 promoting the formation of quinoline 1a with the highest
selectivity.
All these results are in accordance with those previously
reported by us when using (Al)SBA-15 or its Cs-analog, in toluene
as solvent, yielding in both cases mixtures of the corresponding
quinolines 1b and quinolones 2b [4a]. Therefore, we can conclude
that the Friedländer condensation of 3 with 4 is promoted by meso-
porous molecular sieves exhibiting predominantly Lewis acid sites,
(Al)SBA-15, or Brønsted acidity, SBA-15/S, leading to mixtures of
quinoline 1/quinolone 2. Remarkably, when using the hybrid meso-
porous molecular sieve, SBA-15/APS, the reaction yielded quinoline
1a with the highest selectivity.
´
´
˚
˚
shorter for the trans-(2.18 A) than for the cis-isomers (2.28–2.39 A)
O), mainly for 6a (Fig. 6).
(NH···O
C
C shorter than NH···O
C
For 6b, the non-H bonded carbonylic/carboxylic moiety is copla-
nar to the olefin, thus minimizing steric repulsions and maximizing
´
˚
interaction (weak H-bond O···H CH2 , ∼2.2 A) with the carbonylic
substituent in a s-cis conformation (C
C
C
O dihedral angle of 13◦,
for cis-6b) or in a s-trans conformation (dihedral angle of 156◦, for
trans-6b). In these situations, it is expected a close energy between
both isomers of 6b.
On the contrary, for 6a, the phenyl substituent cannot be copla-
nar with the olefin due to steric and electronic repulsions with the
carbonyl/carboxylic ester, also out of the plane. Although stabiliz-
ing weak CH–␲ interactions between the phenyl ␲-cloud and an H
´
˚
of the methyl group (2.65 A) are observed for cis-6a [27], trans-6a
shows the maximum separation between carbonylic oxygen, thus
minimizing strong electronic repulsions (Fig. 6).
The computed enthalpies show that the trans-isomers of 6a
and 6b exhibit a lower value than the cis-counterparts. However,
whereas for 6b the difference in the enthalpy between both iso-
mers is very small (0.63 kcal/mol), it becomes significant for 6a
(3.09 kcal/mol). This result reveals a thermodynamic preference for
3.3. Theoretical calculations
In summary, the condensation of 3a with 4 catalyzed by SBA-
15/S afforded quinoline 1a/quinolone 2a mixture in a ratio 2.7:1

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J. López-Sanz et al. / Catalysis Today 187 (2012) 97–103
Fig. 5. Optimized structures (B3LYP/6-311G(3d,2p)) of the precursors 3a (left) and 3b (right).
Fig. 6. Optimized structures (B3LYP/6-311G(3d,2p)) of the isomers of 6: 6a (bottom), 6b (top), cis-(left), trans-(right).
the formation of the key intermediate trans-6a which would control
the evolution of the reaction to the quinoline 1a and could account
for the experimental ratios.
quinoline 1a. Moreover, we can drive the condensation towards
the formation of quinolone 1a or quinoline 2a as function of the
used catalyst.
Theoretical calculations on the presumed key intermediates
indicate a thermodynamic preference for the formation of the
trans-isomer 6a due to the interplay of subtle steric and electronic
effects which would drive preferentially to the quinoline prod-
uct.
Remarkably, the highest reaction selectivity preferentially to
quinoline 1a is achieved when the condensation is catalyzed
by SBA-15/APS. Comparing with other acid mesoporous cata-
lysts, it suggests the involvement of sulfonic acids over the
catalyst in the reaction, but also probably the amine func-
tions. In this sense, theoretical mechanistic studies are in
progress.
4. Conclusions
In conclusion, mesoporous catalysts here reported were found
to be efficient catalysts for the Friedländer condensation between
2-aminoaryl ketones 3 and ethyl acetoacetate 4 providing the
corresponding quinolines 1/quinolones 2. Acidic mesoporous
catalysts, SBA-15/S and SBA-15/APS, yielded mixtures of the cor-
responding quinolines 1/quinolones 2 whereas basic catalysts,
SBA-15/AP, afforded exclusively quinolone 1b with excellent yield.
Among the acidic catalysts, SBA-15/S was found to be the most
active catalyst, SBA-15/APS being the most selective leading to

J. López-Sanz et al. / Catalysis Today 187 (2012) 97–103
103
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